My 97 Deville Concours (4.6L) has just developed overheating problems within the past month. I had a new radiator installed and all the hoses and connections checked. There are no visible (or smellable) leaks at all, but the overheating persists. (Also there's never been a hint of coolant smell in the cab that would indicate a heater core leak and the heater works fine.) But I'm still having to replace coolant regularly.

Iíve never noticed the car blowing steam from the tailpipes. The insides of the tailpipes are not slimy, thereís just a dry, black soot. (However, Iíve been running straight water in the radiator for the past couple of weeks, since Iím having to replace coolant frequently.) The oil appears to be completely normal.

My radiator mechanic measured for exhaust gases in the coolant twice and could not get the test to turn to yellow for a positive indication of combustion gases in the coolant. He said there was no overheating problem at idle, but when he loaded the engine, it would blow coolant from the overflow tube at the expansion tank.

Other than overheating, the car runs great at all speedsóexactly as before, with no change in power at all.

Here's how the problem presents itself: typically, within about 3 miles the car will reach normal operating temperature (198-220 degrees, temp gauge at 50%). Then, after another 8 miles or so at 2500 rpm (about 78 mph), the gauge makes a run for the red line. About the time the gauge hits 250 degrees (75%), I can flip the temperature control up to 90 degrees (turning the AC off and heater on) and the temperature gauge will come back down to the 50% (normal) position. Usually I can get the gauge to come back to 50% even while maintaining the rpm's at around 2500. Frequently, after getting the gauge back to 50%, I can even turn the AC back on and it will operate just fine.

Maybe it's wishful thinking, but I really don't think it's a head gasket issue. Someone advanced the theory that since this is a common problem with this engine, maybe thereís a design flaw that allows it to develop an air pocket at the thermostat which would cause it to remain closed, resulting in the overheating problem, further positing the idea that an in-line water pump might solve the issue. (I've tested the thermostat...and even drilled two 1/4 holes in the thermostat in an effort to keep such an air pocket from developing. It doesnít seem to have had any effect.)

Any ideasÖI hope?

chubbyranger

06-11-08, 06:00 AM

While it may still be HGs (you are in the 97 - 99 "prone zone") check the water pump belt and tensioner. If adding additional cooling (turning on the heater) corrects the problem and you have replaced the radiator it points toward a circulation issue. Also check to see if the purge line is plugged - that could be causing an air pocket.

Destroyer

06-11-08, 07:18 AM

My '98 did exactly what you describe. It was the head gaskets. Good luck to you.

VinnyT

06-11-08, 09:04 AM

It is the HG. Since your replacing the coolant so often, it may not be circulating enough to absorb the exhaust gases. Thus, no blue-to-yellow indication. My fathers 98 STS does the EXACT same thing. The blue dye turned yellow within 15 seconds. I could easily smell the exhaust in the coolant also.

I used to own a 98 Deville, which was a great car. Unfortunately, my views of these engines are not so positive. :helpless:

rickrus

06-11-08, 09:05 AM

Thanks for the suggestions. The purge line purges water on startup. I'll check the water pump belt this evening. The belt and water pump appear to be operating correctly, but I'll check the tension this evening. I do notice that the belt has a frayed spot on it even though it's only a couple of years old.

krimson_cardnal

06-11-08, 09:30 AM

Circulation issue. Failing water pump in my opinion. Did this begin to show up after the new radiator went in? I would pull the thermo you've "customized" and replace it with the correct OEM for your engine. You are not going to re-engineer the NorthStar cooling system with any success. The water pump is a high flow capacity unit, up to the task at hand.

Suggest a pressure test on the cooling system, failing water pump leak will show up. They are not easy to pinpoint. A combustion gas leak test on the coolant would also be in order to put the failing HG concern to rest. Both can be done in your driveway with proper tools or at a competent radiator shop - same place that installed the radiator. K_C

misfit6794

06-11-08, 11:25 AM

The exhaust gas test most likely wasn't accurate since you've been putting in new coolant so often. The only other way to check for a failed hg is a cylinder leak test. A bad waterpump wouldn't cause such a drastic loss of coolant, a pressure test will show if it is leaking though or if you have an unknown external leak. I believe its the hg's though.

rickrus

06-11-08, 02:45 PM

Circulation issue. Failing water pump in my opinion. Did this begin to show up after the new radiator went in? I would pull the thermo you've "customized" and replace it with the correct OEM for your engine. You are not going to re-engineer the NorthStar cooling system with any success. The water pump is a high flow capacity unit, up to the task at hand.

Suggest a pressure test on the cooling system, failing water pump leak will show up. They are not easy to pinpoint. A combustion gas leak test on the coolant would also be in order to put the failing HG concern to rest. Both can be done in your driveway with proper tools or at a competent radiator shop - same place that installed the radiator. K_C

The coolant loss predates the installation of the new radiator...and continued after the new radiator was installed.

rickrus

06-12-08, 12:30 PM

Anybody care to venture a guess as to the "core value" of a 97 Concours that looks and runs great--and has an hg problem?:horse:

tateos

06-12-08, 02:29 PM

$300?

misfit6794

06-12-08, 05:07 PM

I've seen ones sell for 1000 with a blown headgasket that weren't in that great of shape. You could probably get more money if you parted it out.

Destroyer

06-16-08, 09:22 PM

I've seen ones sell for 1000 with a blown headgasket that weren't in that great of shape. You could probably get more money if you parted it out.I got $1600 for my '98 Deville with blown HG's BUT, I had new '05 polished STS Wheels/tires put on $1000, tinted windows @ $135, new headlights @ $180, coil springs intalled out back $300 and a bunch of other things that I sold with the car. Mine had 98k miles. Looking back, I would have done MUCH better parting it out. Here's a pic of my ex POS:

http://i190.photobucket.com/albums/z251/AstrocreepVIII/98Deville2.jpg

Mark C

06-18-08, 12:26 PM

I wouldn't touch a pre-2000 caddy with HG problems for more than 1K, but I'm cheap. My 97 STS was 995, and my 2000 deville was 500 and it didn't even have a HG issue, just a cracked radiator end box.

rickrus

06-18-08, 10:06 PM

OK...I've run the block test--twice--and the coolant which was tested had been inside the engine for four days, and driven about six times (driven in normal city street traffic twice each day for about 10-15 minutes each trip.) One test was done on about 200 degree water after a 15 minute trip; the next test was done about 10 minutes later, after I had driven up a very steep hill and the coolant gauge had just taken a run for the red line (it was tested when the water was just under the red line at about 260 degrees).

Nothing but blue water both times.

Any further suggestions?

krimson_cardnal

06-18-08, 11:27 PM

Circulation issue. Failing water pump in my opinion. Did this begin to show up after the new radiator went in? I would pull the thermo you've "customized" and replace it with the correct OEM for your engine. You are not going to re-engineer the NorthStar cooling system with any success. The water pump is a high flow capacity unit, up to the task at hand.

Suggest a pressure test on the cooling system, failing water pump leak will show up. They are not easy to pinpoint. A combustion gas leak test on the coolant would also be in order to put the failing HG concern to rest. Both can be done in your driveway with proper tools or at a competent radiator shop - same place that installed the radiator. K_C

Ranger - the test draws free air in the cooling system through a blue indicator liquid and tests for CO2. It turns color if present. CLICK (http://www.cadillacforums.com/forums/northstar-performance-technical-discussion/142490-combustion-leak-detection.html) The test isn't looking for gasses in the coolant, but in the coolant system. Blue is good don't ya know. K_C

Ranger

06-19-08, 04:08 PM

:thumbsup: Thanks

patterson

09-02-08, 01:40 AM

I replaced the water pump belt on my 95 Eldorado today. I found that flexing the tensioner and trying to work a new belt in will damage the belt. Tore the shit out of the one I pulled out. Hence I can't quite smash the new one into place. Luckily, but after a little damage to the new belt, I noticed that the tensioner assembly itself comes loose from it's base plate. (deep 10mm socket) It moves just out of the way allowing the new belt to be strung safely. The tensioner assy. only needs to be loosened up and maneuvered out of the way, not dis-mounted. Loosen one screw much more than the other and twist the tensioner assy. out of the way. But I think you'll find that even when it's loose it must still be flexed with a 0.25" socket driver to get the belt on correctly. ... a $10 belt and 20mins